Phomopsis subordinaria field survey
To characterize the distribution, and drivers, of P. subordinaria, and to measure the relationship between within-host symptom severity and epidemic size and within-population prevalence, we surveyed 260 P. lanceolata populations in early September 2018 for infection by P. subordinaria . These populations were selected to represent different areas in the Ă…land Islands. The field identification of P. subordinaria was confirmed by microscopy of field collected samples consisting of an infected floral stalk. In each population, the epidemic size (measured as number of infected plants), and within-population prevalence (measured as proportion of infected plants within-population) of P. subordinaria infected plants was counted. In each population, we assessed the within-host infection load of the pathogen by counting the proportion of infected flower stalks within each plant from ten infected plants. Host population size is expected to increase infection risk of populations (Parratt et al., 2016) and thus, we estimated the host population size as coverage of the host plant in square meters. Host connectivity was measured in order to understand how distances between host populations may impact pathogen prevalence (Jousimo et al., 2014). Host population connectivity was calculated as